Studies and Snack Breaks

Veterinary technician Evelyn Skoumbourdis and environmental enrichment coordinator Casey Coke Murphy discuss proper feeding of small laboratory mammals

Due to their smaller size and handleability, hamsters, gerbils, guinea pigs and rabbits are widely used in biomedical research studies. According to the US Department of Agriculture (USDA), these species made up more than half of the total population of animals regulated by the agency and used in research studies in 2007. Although popular and well-known to researchers and animal care staff, all of these species have specialized needs when it comes to feeding and nutrition, which can be a hurdle for those attempting to utilize foodstuffs as enrichment. 

Though using foodstuffs as a part of an environmental enrichment program can be rewarding for both the humans and animals involved, there are things that should be addressed prior to starting any type of new enrichment. Always first check with the investigators and veterinary staff to ensure that adding supplementary foods to an animal’s diet will not interfere with the research project or breeding of the animals. Also remember that food enrichment is merely a supplementation to the animal’s diet and should never under any circumstances be used as a sole food source. All supplemental foods should be given in moderation to avoid possible health issues, such as malnutrition, obesity or dental problems.

In the wild, hamsters feed upon seeds, wild grasses and flowers. However, a manufactured hamster diet is nutritionally complete, which means there is no dietary need to supplement in the laboratory. Thus, one must be careful when selecting foods for enrichment supplementation, because the hamster is partial to sweeter foods like fruits, and will consume them in preference to the provided diet, which may lead to malnutrition and/or dental issues (such as malocclusion of the incisors). 

The hamster has several unique physiological attributes that should be taken into account when choosing supplementary foods. The first is that the hamster has cheek pouches (also known as evaginations) that they will use to store and carry food. As hamsters are territorial, they may choose to hold foodstuffs in their pouches if living with others. One should therefore avoid providing any types of food that may become sticky or increase in size due to moisture. Additionally, hamsters hoard food in the wild and will do the same in a laboratory environment, so it is important to remove any uneaten foodstuffs from the cage to keep them from overeating. Finally, processed sugars should be avoided when choosing enrichment foods, as certain strains of hamster are known to spontaneously develop Type 1 diabetes.

In the wild, gerbils consume wormwood, grasses, seeds, bulbs and flowers, and will get their water from greens, as well as dew left upon leaves and grasses. However, in the laboratory it is important to provide gerbils with a nutritionally complete diet and fresh drinking water with which to process the nutrients. Gerbils are known to dig in their bedding throughout the day, and will hoard food. Thus, only small amounts of food should be provided, and all uneaten food should be cleaned from the cage. As is the case with hamsters, this keeps the animal from eating supplemental foods in place of the provided diet, which may lead to malnutrition or malocclusion of the incisors. 

Because they live in open, dusty areas in the wild, gerbils have a naturally high rate of metabolism. However, once placed within the laboratory setting, the gerbil runs the risk of becoming obese and/or developing high cholesterol; preferred foods such as sunflower seeds should therefore be avoided, as they are very high in fat and carry a low nutritional content. 

Guinea Pigs
Although the guinea pig is generally a domesticated species, they will consume green grasses and vegetables when allowed to roam freely, and learn very early in life what foods they require. Due to this early learning, many guinea pigs in the laboratory tend to be neophobic and will only try new foodstuffs after many trials. Thankfully, there are several formulated diets available for use, all of which contain necessary amounts of fat and vitamin C to maintain proper health. Guinea pigs, however, are known to enjoy hays and certain vegetables when added as a supplement to their chow. One must be careful to ensure that the guinea pigs continue to consume their normal diet, not only to avoid scurvy from lack of vitamin C, but because all the teeth of guinea pigs are open-rooted and may overgrow without the proper intake of harder foods, such as chow. 

In the wild, rabbits consume grasses, clover, cultivated plants, fruits, tree bark, twigs and shrubs in order to maintain optimum gut motility and nutrition balance. Manufactured pelleted diets provide the large amount of digestible fiber necessary for the rabbit’s digestive system; but because rabbits in the laboratory are more likely to consume hair, due to higher amounts of shedding and occasional fur chewing, supplementation is often necessary to maintain gut motility. Certain foods with low fiber, like some lettuce varieties, can cause the digestion of the rabbit to become rapid. Since this may result in diarrhea, one should be very careful when selecting greens and other supplementary foods.

Hays such as alfalfa and Timothy have large fiber particles that help to push hair and other indigestible bits along the digestive tract. Feeding items such as these help to maintain motility and avoid impaction of the gut. Other foods like leafy greens and vegetables are also helpful in rabbit digestion. However, when choosing foods, one must be careful not to provide refined sugars or anything starchy, as they can cause an overgrowth of bacteria during the fermentation cycle of the rabbit’s digestion. This bacterial overgrowth can lead to illness and possible enterotoxemia.

About the Authors
Casey Coke Murphy, M.A., R.L.A.T., is the environmental enrichment coordinator for the Division of Animal Care at the Vanderbilt University Medical Center in Nashville, Tenn.
Evelyn Skoumbourdis, M.S., R.L.A.T.G., is a veterinary technician for the Department of Laboratory Animal Services at Thomas Jefferson University in Philadelphia, Pa.

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